Effects of Ionizing Radiation on the EMI-Induced Offset Voltage of Operational Amplifiers

In this work, we investigate the impact of ionising radiation on the robustness towards electromagnetic interference (EMI) of operational amplifiers (OpAmps). Therefore we irradiate two OpAmps, one including a standard differential input stage structure, the other OpAmp featuring a second cross-coupled double differential input pair added to the standard input stage structure. We perform measurements on the manufactured test chip structures to determine general characteristics (gain, offset, gain-bandwidth product (GBWP) and phase margin), as well as EMI-related characteristics like EMI-induced offset and electromagnetic interference rejection ratio (EMIRR). Based on these characteristics, we compare both structures with regard to their performance prior to, during and after irradiation with X-rays. We observe a change in the EMIRR performance with increasing ionising dose. Finally, we explain our observations by taking into account transistor-level effects.